1. Field of the Invention
The present invention relates to an ion implanter, and particularly, relates to an ion implanter for SIMOX (Separation by Implanted Oxygen) which is suitable for implanting oxygen ions into a silicon wafer as an implanting object.
2. Description of the Related Art
Ion implanters which irradiate ion beams from an ion source into a processing chamber to implant oxygen ions to a silicon wafer arranged in the processing chamber, have been conventionally known as a device to implant ions into a silicon wafer. Among this type of ion implanter, Japanese Unexamined Patent Application Publication No. 61-116746, for instance, discloses a device in which a silicon wafer is arranged on a disc-shaped wafer holder and a side of the silicon wafer is held by a holder pin.
A side of a silicon wafer is conventionally held by a holder pin. However, it is not fully considered that particles generate when a silicon wafer is mounted on a silicon holder, and that particles generate due to heat vibration, mechanical vibration or the like during heating of the silicon wafer or ion implantation.
Particularly, when particles accumulate on a silicon wafer in an ion implanter for SIMOX, implantation defects are formed during ion implantation and the defects become pinholes of an insulating layer. Accordingly, insulation of the silicon wafer deteriorates, lowering the quality of the wafer. The particles are generated by various processes such as the mounting process of a silicon wafer onto a wafer holder, heating process, ion implantation process, and the like.
First, during the mounting process of a wafer, a silicon wafer is held still at a specific location by a wafer holding mechanism when the silicon wafer is set on a wafer holder. Thus, friction or rubbing is generated between the wafer and the holding mechanism during the process of holding the silicon wafer still, and particles are generated by friction or rubbing.
On the other hand, in the heating and implanting process, a silicon wafer is initially heated by a heater, and is then heated further by the irradiation of ion beams. When the silicon wafer is heated during the process of heating with ion beams and simultaneously controlling a constant high temperature by adjusting the output of the heater, heat expands the silicon wafer. At the same time, friction or rubbing is generated between the silicon wafer and the holding mechanism, generating particles due to friction or rubbing.
Thus, there is a problem in that particles generate due to friction or rubbing between a silicon wafer and a holding mechanism if the silicon wafer is simply held during a holding process.
As disclosed in Japanese Unexamined Patent Application Publication No. 5-326676, a silicon wafer may be held by a pair of dampers at the sides thereof and simultaneously clamped at constant clamp force while the dampers are held in a rocking manner, to flex the clampers. However, since the dampers are simply flexed when the dampers and the silicon wafer are in contact with each other, friction or rubbing is still generated between each damper and the silicon wafer, depending on the manner or the timing of friction between the damper and the silicon wafer. Accordingly, the possible generation of particles still remains.
Additionally, in an ion implanter which implants oxygen ions or the like into a silicon wafer arranged in a processing chamber by irradiating ion beams from an ion source into the processing chamber, a silicon wafer is supported on a disc-shaped wafer holder as described above. As a wafer holder material, silicon or quartz is used. In other words, the wafer holder is made of the same material as the silicon wafer, such as silicon and quartz, so as to prevent the generation of particles from the wafer holder.
Generally, in an ion implanter, particularly an ion implanter for SIMOX, a wafer holder that is joined to a rotary disk through an arm holder, is rotated at 500 rpm under high temperature of 500xc2x0 C. or higher, and at the same time, is scanned. Oxygen ions are implanted into a silicon wafer on the wafer holder for about four hours in this state, so that it is necessary to prevent foreign matter contamination and the generation of particles. In this case, foreign matter contamination can be prevented by restricting the material of members arranged near the silicon wafer to which ion beams are irradiated. In other words, the same material as the silicon wafer, such as silicon and quartz, can be used as a material for the wafer holder to which ion beams are irradiated while the silicon wafer is held, thereby preventing foreign matter contamination.
However, even if the same material as the silicon wafer, such as silicon and quartz, is used for a wafer holder, silicon and quartz have poor contactability with the silicon wafer, thus generating particles at a contact point between the holder and the wafer.
It is an object of the present invention to provide an ion implanter which can prevent particles generated by holding an implanting object.
In order to solve the above-noted problems, an ion implanter according to a first aspect of the present invention has a processing chamber which forms a processing space for an implanting object in a vacuum atmosphere; an ion beam irradiating means to irradiate an ion beam output from an ion source into the processing chamber; a holding means which is arranged in the processing chamber and movably holds the implanting object; and a carrier means to shift the holding means in a propagation region of an ion beam in the processing chamber as a passing region of the implanting object. Contacting parts of the holding means with the implanting object are rotatable at an axis which is parallel to an axial center of a holder base as a center of rotation.
Since the contacting parts of the holding means with the implanting object are rotatable at the axis which is parallel to the axial center of a holder, the contacting parts rotate when friction or rubbing occurs between the implanting object and the holding means by holding the implanting object with the holding means. Thus, friction or rubbing is avoided, preventing particles from generating.
Specifically, when friction or rubbing is generated between the holding member and a silicon wafer due to heat vibration or mechanical vibration by mounting the silicon wafer as an implanting object on the holder base or by holding a side of the silicon wafer on the holder base with the fixing member and the holding member, the holding member rotates, thus avoiding friction or rubbing between the holding member and the silicon wafer and preventing particles from generating. Accordingly, the quality of the silicon wafer improves.
Furthermore, an ion implanter according to a second aspect of the present invention has a processing chamber which forms a processing space for an implanting object in a vacuum atmosphere; an ion beam irradiating means to irradiate an ion beam output from an ion source into the processing chamber; a holding means which is arranged in the processing chamber and movably holds the implanting object; and a carrier means to shift the holding means in a propagation region of an ion beam in the processing chamber as a passing region of the implanting object. Contacting parts of the holding means with the implanting object are made of a material which has good contactability with the implanting object.
Since a material which has good contactability with the implanting object is used as a material for the contacting parts of the holding means with the implanting object, the implanting object can be rotated at 500 rpm under high temperature of, for instance, 500xc2x0 C. or more. Moreover, even when the ion beam is implanted for about four hours, particles can be prevented from generating from the contacting parts. Accordingly, quality improves.